CEE 626 MASONRY DESIGN Lateral Loads Flexible and Rigid Diaphragms Slide Set 8 Spring 2015

Look first at Out of Plane Loads Need to account for openings The wall spans vertically placing a load on the floor or roof diaphragm Diaphragm reaction The wind load transfers a reaction To the top and bottom Wind load generally uniform except at corners for low rise buildings How is load at diaphragm transferred to resisting elements (shear walls)? Depends on whether diaphragm flexible or Rigid V V Shear walls Shear walls Wind load generally uniform except at corners for low rise buildings at diaphragm level

Shear Walls and Diaphragms Whether a Diaphragm is “Rigid” or “Flexible” depends on the relative stiffness of the diaphragm and the shear walls. ASCE7 Says Diaphragm Deflection <2 x Shear wall deflection – You can consider diaphragm rigid

Shear Walls and Diaphragms Generally concrete slabs are rigid and steel and wood systems are flexible diaphragms. However, some low aspect ratio wood and steel diaphragms are semi-rigid. This is beyond the scope of this course but most designers would look at these as a flexible and then as Rigid then design for the worst case – see ncma.org – TECK14-12-B– bia.org –Tech note 24c

Shear Walls and Diaphragms Plan view at diaphragm level

Shear Walls and Diaphragms Plan view at diaphragm level d=L1/2 Note this is approximate and does not account for Shear deformations of metal and wood panel slip

Shear Walls and Diaphragms

Shear Walls and Diaphragms For instance a 8” CMU wall for a 12.7’ height (h/t = 20) can allow a deflection of .00533 x7.625 = .041” (for Ft +fa = 20 psi)

Shear Walls and Diaphragms

Shear Walls and Diaphragms However most walls not fully grouted and have flashing at base – It is best to assume Pin-Pin supports for walls out of plane

Shear Walls and Diaphragms

Shear Walls and Diaphragms

Shear Walls and Diaphragms

Shear Walls and Diaphragms Once you distribute the Loads to a shear wall line in a flexible diaphgram system you must then distribute the shear to each shear wall element in the line. Code say this is done w.r.t. relative rigidities Perforated Shear walls Load on a shear wall line V distributed to Shear wall elements Vi V = S Vi and Dis tribute w.r.t to relative rigidities of elements Vi V V Vi Shear walls Shear walls

Shear Walls and Diaphragms Must look first at deformation of shear wall elements (Slides from Dan Abrams Class Notes)

Shear Walls and Diaphragms Fixed - Fixed

Shear Walls and Diaphragms

Shear Walls and Diaphragms

Shear Walls and Diaphragms 19

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Shear Walls and Diaphragms There are a number of methods to address load distribution for shear walls with various sized openings (see Schnieder and Dickey, The MDG 4 etc). These help address the issue where you may have a condition that suggests a section with openings will be stiffer than a section without. If it gets complicated – Usually use Finite Element analysis.

Shear Walls and Diaphragms

Shear Walls and Diaphragms Assume all are fixed-fixed Code 1.9.4.2.3 beff = 6t Compression and 1/2h tension

Multi-story shear walls in a line also have effects of overturning adding axial load on top of shear wall segments Do Solid 2 story wall on Board

Shear Walls and Diaphragms Multi-story shear walls in a line also have effects of overturning adding axial load on top of shear wall segments

Shear Walls and Diaphragms Multi-story shear walls in a line also have effects of overturning adding axial load on top of shear wall segments

Shear Walls and Diaphragms Additional axial load on shear wall segments small and neglected on low rise single story buildings . Only an issue where shear walls are broken up with openings along a given line –”Perforated Shear Walls” – “to account for moments from above”. Normally ignore in one story walls.

Shear Walls and Diaphragms

Shear Walls and Diaphragms

Shear Walls and Diaphragms (PCL)

Shear Walls and Diaphragms Look at lowest level

Shear Walls and Diaphragms Look at lowest level

Shear Walls and Diaphragms

Shear Walls and Diaphragms

Shear Walls and Diaphragms

Shear Walls and Diaphragms

Shear Walls and Diaphragms Note the negative signs are reversed

Perforated Shear Walls You would then design the segments for the appropriate load combinations for either ASD or SD as before. Note there is a discrepancy in the pier c analysis - K , V and M is based on full height and P is base at opening height it is conservative to assume Peq is applied at the top of this pier, even though it is calculated at the opening height.

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Shear Walls and Diaphragms Now on to Rigid Diaphragms Diaphragms diaphragm flexible or Rigid V V Shear walls

Shear Walls and Diaphragms

Shear Walls and Diaphragms

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Shear Walls and Diaphragms

Shear Walls and Diaphragms ± ±

Shear Walls and Diaphragms Additional Flexible and Rigid Diaphragm designs with segmented and perforated shear walls will follow.